The present invention relates to high power lasers of the type described in U.S. Pat. No. 3,702,973 granted Nov. 14, 1972 wherein the apparatus comprises a gas laser and an electron source for initiating and maintaining the lasing condition.
In an electron beam stabilized gas laser, there are two contiguous chambers, one in and/or through which the laser medium flows depending on the type of laser construction--the main or sustainer cahmber--and the other in which the electron beam is generated--the accelerator chamber. These two chambers are separated by an electron transparent, gas impervious diaphragm usually a pinhole free, aluminum foil of 0.1 to 0.5 mils thickness. The accelerator chamber must be pumped down to and maintained at a hard vacuum level--about 10 Torr. On the other hand, the main or sustainer chamber is pumped down to the working pressure of the laser gas, about 1/10 of an atmosphere (50 to 100 Torr). In steady-state operation, there is, therefore, an expected pressure difference of about 1/10 atmosphere across the diaphragm. The diaphragm is designed to withstand this expected pressure differential, but is not designed to withstand a substantially greater pressure differential. This design limitation is imposed to avoid greater thickness than necessary since, for a given voltage, fewer electrons would pass through a thicker foil or other diaphragm into the chamber resulting in a lowering of the upper limit on the power in the laser beam. Alternately, to cause the same number of electrons to pass through a thicker foil diaphragm, a higher voltage would have to be applied. This would, in turn, cause harder X-rays to be generated. If the foil ruptures, it has to be changed; this involves air release and the loss of several hours required to replace a diaphragm. In many operations, continuous maintenance of such laser equipment under vacuum is desired. The foil is also simultaneously subject to other failure-inducing mechanisms, i.e. vibrations and thermal stress, as described in said U.S. patent and in co-pending patent application Ser. No. 303,241 filed Nov. 2, 1972, now Patent No. 3,808,551 of common assignment with this application and which disclosure is incorporated herein by reference as though set out at length herein.
It is an important object of the invention to enable provision of very thin foils or other diaphragm means for separation of the two chambers.
It is a further object of the invention to reduce the necessary accelerating voltage for a laser apparatus of the class described consistent with the preceding object.
It is a further object of the invention to reduce incidental X-ray generation in gas laser apparatus of the class described consistent with one or both of the preceding objects.
It is a further object of the invention to maintain rapid pumpdown and backfilling cycles consistent with one or more of the preceding objects.
It is a further object of the invention to extend diaphragm life in gas laser apparatus of the class described consistent with one or more of the preceding objects.
It is a further object of the invention to reduce the incidence of diaphragm repair or replacement, and consequent laser shutdown, consistent with one or more of the preceding objects.
It is a further object of the invention to avoid inadvertent production of reverse pressure differentials across the foil or other faulty sequencing of evacuation and backfill schedules consistent with one or more of the preceding objects.
It is a further object of the invention to utilize minimal control apparatus consistent with one or more of the preceding objects.
It is a further object of the invention to reduce the number of measuring instruments involved to reduce expense and cross-calibration dependence, consistent with one or more of the preceding objects.
It is a further object of the invention to provide a multiple monitoring and control functions in a single instrument consistent with one or more of the preceding objects.